Lesson 4 of 9 · 12 min
Lenses
A lens decides how much of the world the camera sees, and how deep or flat that world feels. Most people think a long lens "squashes" the background. The truth is more useful: the distance of the camera does it. The lens only decides how much you crop.
In this lesson
- Say what focal length and field of view are.
- See why perspective comes from camera distance, not from the lens.
- Control depth of field with aperture, focal length and distance.
Try it Change the lens
Start in Keep her size mode. When you change the lens, the camera moves back or forward so that she stays a medium shot. Go from 14 mm to 200 mm and watch the street behind her. Then change to Zoom mode, where the camera stays still, and do it again. Last, change the aperture.
- Keep her size with an 18 mm lens or wider. Look at the street.
- Keep her size with a 135 mm lens or longer. Where did the buildings go?
- In Zoom mode, go to 100 mm. Is the background "compressed", or only bigger?
- Isolate her: a long lens (70 mm or more) at f/2 or f/1.4.
The name for it Focal length and perspective
- Focal length
- A number in millimetres on the lens. A small number (14–24 mm) sees a wide view. A big number (85–200 mm) sees a narrow view.
- Field of view
- The angle the camera sees. It depends on focal length and sensor size. On a Super 35 cinema camera, about 35 mm feels "normal". On a full-frame camera, about 50 mm feels normal.
- Wide-angle lens
- Lets you be close and still see a lot. Space feels deep and stretched. Close faces bulge. Good for energy, chaos and big places.
- Long lens Telephoto
- Lets you be far away. The background looks big and close to the subject. Good for isolation, spying, and crowds that look packed.
If you zoom in and move the camera at the same time, the background seems to grow or shrink around a subject who stays the same size. This is the dolly zoom, made famous by Vertigo (1958) and Jaws (1975). You will try it in the movement lesson.
Depth of field
Depth of field is how much of the scene, from near to far, looks sharp. Three things control it:
- Aperture. A small f-number (f/1.4) is a wide opening: shallow focus. A big f-number (f/16) is a small opening: deep focus.
- Focal length. At the same distance, a long lens gives less depth of field.
- Distance to the subject. The closer the focus, the shallower the depth of field.
Shallow focus tells the audience where to look and separates a person from the world. Deep focus lets the audience choose where to look and keeps people in their world. Citizen Kane (1941) is famous for deep focus.
On set, the focus puller (the first assistant camera) keeps the subject sharp. Moving focus from one subject to another during a shot is a rack focus or focus pull.
Check Four questions
You stand still and zoom from 35 mm to 100 mm. What happens to perspective (the size of the buildings compared with the actor)?
Perspective depends on where the camera is. Same place, same perspective.
Which gives the shallowest depth of field?
Long lens, wide aperture and close focus all make depth of field shallower.
A car chase needs to feel wild and fast, with the camera close to the action. Which lens is a good start?
A wide lens close to the action stretches space and makes movement toward the camera feel fast.
What is a rack focus?
A rack focus moves the audience's attention without a cut.
Field exercise Guess the lens
With your phone, take two photos of a friend standing in front of a street: one close with the wide lens, and one from far away with the zoom lens, so that your friend is the same size. Put the photos side by side. That is what this lesson is about.